1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device having an aluminum/germanium alloy film (Al/Ge alloy film) forming a wiring layer in the semiconductor device and, more particularly, to a method of removing germanium (Ge) particles precipitated in an Al/Ge alloy film in fabricating a semiconductor device.
2. Description of the Prior Art
Miniaturization of a semiconductor integrated circuit requires a wiring conductive film to be formed flat on a layer insulating film and to perfectly fill up contact holes formed in the layer of insulating film. It is important that the wiring conductive film is formed at a relatively low temperature.
A method of forming such a wiring conductive film employs a sputtering process in which a substrate is heated at a relatively low temperature on the order of 300.degree. C. and which deposits an aluminum/germanium alloy (Al/Ge alloy) of a Ge concentration on the order of 5%. During the sputtering process, particles of the Al/Ge alloy deposited on the layer of insulating film melt and the molten Al/Ge alloy flows and fills up the contact holes formed in the layer of insulating film, and the surface tension makes the molten Al/Ge alloy form an Al/Ge alloy film having a flat surface. Since the Al/Ge alloy film is formed at a relatively low film forming temperature, aluminum (Al) does not permeate the substrate during the Al/Ge alloy film forming process and hence junction breakdown does not occur. Accordingly, any barrier metal film, such as a titanium film or a titanium nitride film, need not be formed before forming the Al/Ge alloy film.
In forming the Al/Ge alloy film by the foregoing method, surplus Ge precipitates in the Al/Ge alloy film because the solid solubility of Ge in an Al/Ge alloy is as small as 1.5%. The particle size of the precipitated Ge particles is on the order of 1 .mu.m at a maximum, which causes the following problems in submicron processes.
Submicron contact holes are clogged with the precipitated Ge particles of a particle size on the order of 1 .mu.m, thereby increasing the resistance of the contacts and, in the worst case, no contact is formed in the contact holes. The current flow passage area of the wiring lines of a width less than 1 .mu.m is reduced by Ge particles (nonconducting particles) having a particle size nearly equal to the width of the wiring lines to deteriorate migration resistance. Ge particles precipitated during the formation of an Al/Ge alloy film cause problems in patterning the Al/Ge alloy film in a wiring pattern. Although it is possible to reduce the Ge concentration to 1.5%, the reduction of the Ge concentration is unable to solve fundamental problems because Ge particles precipitate while the temperature of the Al/Ge alloy film drops from the film forming temperature of 300.degree. C.